Mowing and rollingstrategies to manageanthracnose on annualbluegrass greensIncreased mowing frequency and lightweight rollinghelpsuperintendents rise above anthracnose epidemics andmaintain green speed.

Anthracnose, caused by the fungus Colleto-trichum cereale (2), has become a common dis-ease of annual bluegrass (Poa annua) and, to alesser extent, creeping bentgrass (Agrostis stolon-ifera) greens throughout the world (9). The dis-ease may occur as a basal rot of necrotic, water-soaked crown tissue at any time of the year or asa foliar blight during high summer temperatures(17). Both types of anthracnose typically startas 0.25-' to 0.50-inch (0.64- to 1.27-centimeter)chlorotic (yellow) patches that coalesce to affectlarger areas of turf. Black to brown reproductivestructures (acervuli) containing crescent-shaped,single-celled spores and hairlike spines (setae) oninfested tissue are diagnostic signs used to identifythis disease.

Control of anthracnose epidemics is compli-cated. Many parts of the country have reportedthe presence on greens of C. cereale isolates thatare resistant to a number of fungicide classes thathave suppressed anthracnose in the past (9). Fur-thermore, anthracnose is more severe on stressedturf (9), and cultural practices employed toimprove playability (that is, green speed or ball-roll distance) are thought to enhance this diseaseby increasing plant stress. Insufficient nitrogenfertilization is known to increase anthracnoseseverity on annual bluegrass greens (4). However,it is not known how other cultural practices usedto manage green speed affect anthracnose severity.

Mowing height is inversely related to greenspeed, a common measure of putting green play-

ability (8). Cursory studies have demonstratedthat anthracnose incidence and severity increasesat lower heights of cut (1,10), although we haveyet to determine the effects of mowing heightcombined with different mowing frequenciesor lightweight rolling on anthracnose and greenspeed. Mowing frequency can be increased (thatis, daily double-cut) to improve green speed (8).However, increased mowing frequency mayreduce root mass and carbohydrate reserves (5)and increase damage (wounding) to leaf tissues,possibly enhancing infection by C. cereale (9).

Lightweight rolling is another practice used toincrease green speed by smoothing and improvinguniformity of the .turf canopy (8). Rolling morethan three times per week reduced turf quality in

Anthracnose generally begins as 0.25- to 0.50-inch chlorotic(yellow) patches that coalesce to affect larger areas of turf.Photos by J. Inguagiato

• •• •:.. :..

/ ~Environmental

Institute for Golf~ ~

This research was funded in partby The Environmental Institute forGolf and the United States GolfAssociation.

John C. Inguagiato, Ph.D.James A. Murphy, Ph.D.Bruce B. Clarke, Ph.D.

May 2009 GeM 111

• •• •• •• •• • ••

Lightweight rolling + mowing height, 2004

Aug.2TreatmentMowing height0.110 inch 4.2

Aug.11 Aug.23% anthracnose disease

Sept. 15

36.8 51.7 61.853.644.5

0.125 inch0.141 inch

2.6,__ ---t__ -.:.- -+ -+- ---:...j

1.1LSD (0.05)t - -.1- _2.2

Lightweight rollingnoneevery other day

3.0----1---2.3

LSD (0.05)t 0.5

32.228.8

48.040.5

NS 8.8 7.3

34.231.0

3.2

--r~__49.0 . .-r 44.456.250.4

NS 3.9

tLSD (least significant difference). The difference between two means (within the same column for each main effect) must be greaterthan the LSD to be considered statistically different.

Table 1. Anthracnose disease severity response to mowing height and lightweight rolling on annual bluegrass turf in North Brunswick,N.J., in 2004. These data are representative of treatment effects observed in 2004 and 2005.

Lightweight vibratory rolling (left) and mowing practices (right) were tested to determine their effecton anthracnose and putting green speed.

some research studies but had no effect in others(8). The effect of lightweight rolling on anthrac-nose is unknown, although it may enhance dis-ease severity (9).

The impact of increased mowing frequencyand lightweight rolling on anthracnose needs tobe determined. Moreover, it may be possible toreduce anthracnose severity by slightly raising themowing height while maintaining green speedwith more frequent mowing and/or rolling. Thus,

112 GeM May 2009

the objectives of this field trial were to evaluatemowing height, mowing frequency, lightweightrolling and the potential interaction effects onanthracnose severity and green speed of annualbluegrass maintained as putting green turf.

Materials and methodsA two-year field trial was initiated in 2004 on

annual bluegrass turf grown on a sandy loam andmaintained as putting green turf in North Bruns-wick, N.]. Nitrogen was applied to the trial 19times from March to November 2004, totaling3.5 poundsll,OOO square feet/year (17.1 grams/square meter/year) and 11 times from March toAugust 2005, totaling 1.6 pounds/1,000 squarefeet/year (7.8 grams/square meter/year). Phospho-rous and potassium were applied based on soil-testresults.

The trial was lightly. topdressed with mediumsand, which was incorporated with a cocoa-matdrag every 14 days. To maintain relatively dry soilconditions, irrigation was applied only when wiltstress was evident and when washing-in fertilizer.Primo Maxx 1MEC (trinexapac-ethyl, Syngenta)was applied at 0.125 fluid ounce/1,000 square feet(0.04 milliliters/square meter) every 14 days fromApril to October each year.

Diseases other than anthracnose and variousinsect pests were controlled preventively eachyear; fungicides not effective against the anthrac-nose pathogen (4) such as Emerald (boscalid,BASF), Curalan (vinclozolin, BASF) and ProStar

• •• •• •• •• • ••research

(flutolanil, Bayer Environmental Science) wereused during the growing season.

Treatment designMowing height treatments were bench set-

tings of 0.110, 0.125 or 0.141 inch (2.8, 3.2 or 3.6millimeters) on a walk-behind mower equippedwith a grooved front roller. Mowing frequencytreatments consisted of mowing seven or 14 timesper week (that is, once or twice daily). Mowingtreatments were performed between 8 a.m. and9:30 a.m. each day. Lightweight rolling includeda treatment with no rolling or one pass every otherday immediately after mowing with a vibratoryroller attached to a triplex mower. All possiblecombinations of mowing height, mowing fre-quency and lightweight rolling were evaluated.

Results and discussionAnthracnose severity

Anthracnose basal rot symptoms first appearedon July 29, 2004. The field was inoculated onAug. 2 to improve uniformity of the infestation,and the disease gradually increased in severity toa moderate level (45%-62%) in mid-September(Table 1). Disease developed earlier in 2005 (June15) as a natural infestation and progressed slowlybefore dramatically increasing to severe levels(79%-92%) by Aug. 16, 2005. Treatment effectson anthracnose severity were similar during bothyears; therefore, we present only 2004 data, whichis representative of both years.

Mowing heightAs expected, mowing height had the most

pronounced effect on anthracnose throughoutthe study, frequently increasing disease severityat lower heights. Mowing at 0.110 inch increaseddisease severity 3% to 17% in 2004 (Table 1) and13% to 21% in 2005 (data not shown) comparedto 0.141 inch (Table 1). Turf mowed at 0.125 inchhad 8% to 10% less disease than turf mowed at0.110 inch, but 5% to 9% more disease than turfmowed at 0.141 inch on the last observation dateeach year (Table 1). Previous reports have alsoindicated that lower mowing heights increaseanthracnose severity (1,10); however, these studiesevaluated much greater incremental differences inmowing height (10) or a greater mowing heightrange (1).

Data from our trial indicate that relativelysmall increases in mowing height (0.015 inch)at low heights of cut (0.110 to 0.125 inch) canreduce anthracnose severity. Routine mowing,particularly at reduced heights, can stress plantsby removing photosynthetic tissue and severing

- ~=:=====~-----Anthracnose severity response, 2004

Mowing frequency/week7 14

Mowing height (inch)

0.110

0.125

0,141

60,6aA

47.1bA

60.0atN 63,6aA

46.5bB

41.9bA

tMeans within columns followed by the same lowercase letter are not significantly different.~Means within rows followed by the same uppercase letter are not significantly different.

Table 2. Anthracnose disease severity response to mowing height and mowing frequency onannual bluegrass turf in North Brunswick, N.J., on Sept. 15,2004.

protectivecuticular layers.Mainta:ing Ke~t~c:: rbluegrass (Poa pratensis) at lower mowing heights(that is, greater defoliation) can reduce carbohy-drates and enhance summer patch (3) and melt-ing-out diseases (7). Lower mowing heights canalso reduce root mass (5) and depth (6) and tol- I

erance of turfgrasses to environ~ental stress (6).Carbohydrates, root mass and depth may havebeen enhanced at increased mowing heights inour trial, thus reducing plant stress and improvingtolerance to anthracnose.

Mowing frequencyMowing frequency generally had little or no

effect on anthracnose severity (data not shown).Mowing turf 14 times per week did occasionally(twice during the two-year study, including Sept.15, 2004) reduce disease severity of turf mowedat 0.125 inch (Table 2), although this effect wasrather small and not consistent between years.In the past, limiting mowing frequency has beenrecommended to reduce anthracnose severitybecause the disease was thought to be intensi-fied by wounding stress (9). However, data fromthe current trial indicates that increased mowingfrequency had no negative effect on anthracnose,occasionally reducing disease, particularly in turfmowed at 0.125 inch. Frequent mowing of turfis necessary at low mowing heights to increaseshoot density and avoid scalping damage. Thus,frequent mowing may enhance tolerance of turf I

to low mowing heights (for example, 0.125 inch)and reduce the tendency for scalping injury,

May 2009 GeM 113

• •• •• •• •• • ••_ research

Anthracnose was less severe when turf was mowed at 0.141 inch (left) than at 0.110 inch (right).

I-:rebyminimizing stress and occasionally reduc-I ;~; anthracnose severity. Note that, in practice,increased mowing frequency would increase traf-fic (from turning of equipment) along the perime-ter of the greens, which could increase wear stress.

Lightweight rollingRolling every other day slightly reduced

anthracnose severity (5% to 6%) under moderatedisease pressure (Table 1). Admittedly, the reduc-tion in anthracnose severity caused by rolling wassubtle and probably would be difficult to perceiveon the golf course. However, these data indicatethat rolling does not enhance disease severity aspreviously suggested (9). Rolling has been shownto reduce dollar spot disease on creeping bent-grass greens (8). Furthermore, routine rolling canlimit the gradual elevation of plant crowns (puffi-ness) at the thatch/soil surface during the grow-Iing season, which could reduce the amount of leafblade and leaf sheath tissue removed or damagedat low mowing heights. This rolling effect mayalso enhance photosynthetic capacity because theyoungest leaf blades, which would be most oftenremoved by mowing, are the most photosyntheti-cally active portion of leaves (l I), Additionally,maintaining the position of crowns lower in themat layer may reduce their exposure to high tem-perature stress since temperatures are often great-est at the surface of dense, short-mowed turf.In addition, the response to mowing frequencyobserved in this trial may be related, at least in

. part, to a rolling effect because the large drive

114 GeM May 2009

roller of the walk-behind mower effectively rolledthe turf twice as it was being double-cut.

Green speedPreferred green speed for daily play ranges

from ll4 to 126 inches (9.5 to 10.5 feet) forgreens in the northeastern United States. Mow- .ing heights less than 0.125 inch are commonlyused to achieve this desired speed; turf mowedat 0.1l0 inch seven times per week without roll-ing produced green speeds of 9.5 to 10.5 feet 64%of the time (or ~9.5 feet 82% of the time) (Table3). Similarly, plots mowed 14 times per week, orturf rolled every other day, regardless of mowingheight, produced green speeds at or above 9.5 to10.5 feet 73% to 100% of the time (Table 3). Turfmowed at 0.110 or 0.125 inch 14 times per weekwith or without rolling, and turf mowed at 0.141

I inch 14 times per week and rolled every other dayhad an average green speed that was 7.9 to 15.7

I inches greater than that of turf mowed at 0.110inch seven times per week without rolling (con-sidered a standard practice on annual bluegrassgreens for this study; Table .3). Mowing at 0.125inch seven times per week with or without roll-ing, and mowing at 0.141 inch 14 times per weekwithout rolling, or seven times per week with roll-ing produced an average green speed like that ofturf mowed at 0.110 inch seven times per weekwithout rolling. Only turf mowed at 0.141 inchseven times per week without rolling resulted inan average green speed less (7.9 inches less) thanthat of turf mowed at 0.110 inch seven times perweek without rolling.

Although the average speed of turf mowed at0.125 inch seven times per week without rollingwas not different from mowing at 0.110 inch seventimes per week without rolling, the relatively largefrequency (36%) when speeds were in the range of8.5 to 9.5 feet (102 to ll4 inches) indicated thatthe consistency of green speed with this mowingregime would be undesirable. These data indicatedthat a green speed of 9.5 to 10.5 feet or greatercan be achieved at higher mowing heights (thatis, 0.125 and 0.141 inch, respectively) by increas-ing daily mowing frequency and/or rolling everyother day, practices that did not enhance and, insome cases, reduced anthracnose severity.

Soil bulk densitySoil bulk density was low to moderate dur-

ing the study (data not shown) and was affectedmore often by mowing frequency than rolling ormowing height. Mowing 14 times per week sub-tly increased soil bulk density (2%) compared tomowing seven times per week on four of six dates

• •• •• •••••• •research

Freguenc~ distribution of _reen speeds, 2004 and 2005

Ughtweightrolling/day

Mowing heightOnch)

0,110 7 none 18 64 0 0

0,110 7 every other 0 5 59 0 0 124

0,110 14 none 0 0 14 27 9 136*

0.110 14 every other 0 0 5 55 41 0 137*

0.125 7 none 0 36 59 5 0 0 117

0,125 7 every other 0 0 23 73 5 0 122-----_._- ._-0,125 14 none 0 0 23 73 5 0 128*

---0.125 14 every other 0 0 23 59 18 0 131 *

0.141 7 none 5 64 32 0 0 0 111 *

0,141 7 every other 0 27 73 0 0 0 117

0.141 14 none 0 5 59 36 0 0 124------- ___·_n._._n .. _____ n"n. ____ n_n ___

0.141 14 every other 0 0 50 45 5 0 126*

tAverage green speed of 22 observations made during 2004 and 2005 for each treatment combination,*The average green speed is significantly different from 120 inches, the average speed obtained by mowing at 0,110 inch every seven days without rolling in 2004 and 2005.

Table 3, Frequency distribution (n = 22 observations) of average green speeds obtained from all combinations of mowing height, mowing frequency and lightweight rolling onannual bluegrass turf in North Brunswick, N,J., in 2004 and 2005,

during the trial (data not shown). However, thisincrease in soil bulk density did not appear to beassociated with turf performance. Turf qualityand disease severity were unaffected by mowingfrequency when differences in soil bulk densitywere observed. Furthermore, overall soil bulkdensity declined between September 2004 andJune 2005 (data not shown). Increased soil bulkdensity caused by increased mowing frequencyprobably could be readily ameliorated by routinehollow-tine cultivation or freeze-thaw cycles incool temperate climates.

ConclusionsAs expected, increasing mowing height

reduced anthracnose severity. A relatively smallincrease (O.OIS-inch bench setting) in mowingheight can reduce disease severity by as much as17%. However, contrary to expectations, increas-ing mowing frequency to twice per day did notincrease - and occasionally reduced - anthrac-nose severity, and rolling provided a subtle reduc-tion in disease severity under moderate diseasepressure. These effects of mowing twice per day

and rolling are notable to superintendents whoare attempting to provide acceptable playabil-ity (green speed) without increasing anthracnoseseverity. Mowing twice per day was as effectiveat increasing green speed as lowering the mow-ing height from 0.141 to 0.110 inch; rolling alsoincreased speeds.

Thus, anthracnose severity on annual blue-grass putting greens can be reduced by raising themowing height as little as 0.015 inch, and play-ability (green speed of 9.5 to 10.5 feet or greater)can be maintained by adjustments in other man-agement practices such as increasing mowing fre-quency and/ or rolling without increasing (in soinecases, reducing) anthracnose severity, These datado not suggest that rolling or increasing mow-ing height or frequency will necessarily achieveacceptable control of anthracnose disease in theabsence of an effective fungicide program. How-ever, a comprehensive management program inte-grating these practices with moderate nitrogenfertility may reduce the quantity and/or increasethe application interval of fungicides required to t

provide commercially acceptable disease control.

May 2009 GeM 115

• • • •• •• •• •• •

~ Increasing mowing heightby as little as 0.015 inch can reduceanthracnose severity, and increasingmowing frequency to twice per daydid not increase anthracnose severity.

~ Rolling provided a subtlereduction in disease severity undermoderate disease pressure and alsoincreased green speed.

~ Playability can be maintainedby increasing mowing frequency and/or rolling without increasing anthrac-nose severity.

~ A comprehensive manage-ment program integrating thesepractices with moderate nitrogenfertility may reduce the quantity and/or increase the application interval offungicides required to provide accept-able disease control.

Numerous combinations of mowing height. mowing frequency andlightweight rolling routinely produced green speeds of 9.5 to 10.5feet before anthracnose symptoms developed.

FundingThis work was supported by the New Jersey Agricultural.

Experiment Station, State and Hatch Act Funds, Rutgers Centerfor Turfgrass Science and other grants and gifts. Additional sup-port was received from The Environmental Institute for Golf, GCSA

I of New Jersey, United States Golf Association and Tri-State TurfResearch Foundation.

5. Juska, F.v., and A.A. Hanson. 1961. Effectsof interval and height of mowing on growth ofMerion and common Kentucky bluegrass (Poapratensis L). Agronomy JoumaI53:385-388.6. Liu, X., and B. Huang. 2002. Mowingeffects on root production, growth, and mor-tality of creeping bentgrass. Crop Science42:1241-1250.7. Lukens, R.J. 1970. Melting-out of Kentuckybluegrass, a low sugar disease. Phytopathology60:1276-1278.8. Nikolai, lA. 2005. The superintendent'sguide to controlling putting green speed. JohnWiley & Sons, Hoboken, N.J.9. Smiley, RW., P.H. Oernoeden and B.B.Clarke. 2005. Compendium of turfgrass dis-eases. 3rd ed. The American Phytopathologi-cal Society, St. Paul, Minn.10. Uddin, w., M.D. Soika and O. Livingston.2008. Vertical mowing and mowing heightaffect anthracnose basal rot. Golf Course Man-agement76:84-87.11. Youngner, V.B. 1969. Physiology of growthand development. In: A.A. Hanson and F.v.Juska, eds. Turfgrass science. American Soci-ety of Agronomy, Madison, Wis.

John C. Inguagiato (john.inguagiato@uconn.edu) is apostdoctoral fellow in the department of plant science,University of Connecticut, Storrs; James A. Murphy and BruceB. Clarke are Extension specialists in the department of plantbiology and pathology, Rutgers University, New Brunswick, N.J.

Literature cited1. Backman, P., G. Stahnke and E. Miltner. 2002. Anthracnose

update: cultural practices affect spread of disease in north-west. Turfgrass Trends October:1-4.

2. Crouch, J.A., B.B. Clarke and B.I. Hillman. 2006. Unravelingevolutionary relationships among the divergent lineages ofColletotrichum causing anthracnose disease in turfgrass andcorn. Phytopathology 96:46-60.

3. Davis, O.B., and P.H. Oernoeden. 1991. Summer patch andKentucky bluegrass quality as influenced by cultural practices.Agronomy JoumaI83:670-677.

4. Inguagiato, J.C., J.A. Murphy and B.B. Clarke. 2008. Anthrac-nose severity on annual bluegrass influenced by nitrogen fer-tilization, growth regulators, and verticutting. Crop Science48:1595-1607.

11-& GCM May 2009